This invention relates to a photosensing device comprising a plurality of photosensing elements, especially photovoltaic elements arrayed on a substrate.
A device, for example, a photo-coupler comprising a light emitting part and a photovoltaic part connected by a guiding part can be used for signal transmission under an electrically insulated condition to serve the purpose of energy transmission by means of electricity-light-electricity conversion.
FIG. 1 is a schematic sectional view of one form of such a photo-coupler. Referring to FIG. 1, the photo-coupler comprises a light source or light emitting part 1 including a plurality of light emitting diodes 8 arrayed on a substrate, and a photovoltaic part 2 including a plurality of photovoltaic elements 9 such as solar battery elements or solar cells arrayed on a substrate. The light emitting part 1 and the photovoltaic part 2 are optically coupled by a light guiding part 3 made of a glass, ceramic or like electrical insulator which is used to attain desired electrical insulation as well as desired physical coupling. In this guiding part 3, a specifically designed separate guide path 3' made of an optical glass or similar light transmitting material may be disposed so as to improve the transmission efficiency of light directed from the light emitting part 1 toward the photovoltaic part 2. Numerals 4,4' and 5,5' designate electrode leads connected to the light emitting part 1 and photovoltaic part 2 respectively, and numerals 6 and 7 designate mounts.
A photo-coupler such as that shown in FIG. 1 can be used for the purpose of supplying power to an electrically insulated electronic device, and many light emitting diodes are integrated in its light emitting part 1. A representative light emitting diode employed for the light emitting purpose generates optical output power of 50 mW at a wavelength of 800 nm. It is therefore required to integrate such diodes by the number of 40 so as to provide desired optical output power of, for example, 2 W.
By use of an optical guide such as that shown in FIG. 1, about 40% of the optical output power of 2 W can be transmitted from the light emitting part 1 to the photovoltaic part 2. However, as is commonly known, the improvement in the light transmission efficiency results generally in a nonuniform irradiance distribution at the photosensing part 2.
On the other hand, a voltage as high as, for example, 5 V is required for supplying operating power to the electronic device when the electronic devide is designed for processing of digital signals. Because of the peculiar properties of solar battery elements, a single solar battery element of, for example, silicon can only generate an output voltage as high as about 0.5 V at the most, and even a single solar battery element of gallium arsenide can only generate an output voltage of about 0.7 V. It is therefore necessary to connect many solar battery elements in series for attaining the desired output voltage level of 5 V.
It may be considered that solar battery elements having a rectangular shape as shown in FIG. 2 can be most easily industrially produced. FIG. 2 shows that a plurality of rectangular solar battery elements 21 are disposed in a circular light receiving surface 23. However, such an arrangement gives rise to various drawbacks which will be pointed out presently. Since the solar battery elements 21 are used under the condition of high irradiance or solar radiations, a grid electrode (not shown) is generally formed on the front surface of each of theelements 21 for the purpose of decreasing the surface resistance. Such a front surface electrode of each element is electrically connected to a back surface electrode of the next adjacent element, so that all the solar battery elements are electrically connected in series with each other. Further, it is necessary to define a gap 22 of suitable dimensions between the adjacent solar battery elements 21 so that the elements 21 may not short-circuit with one another. Consequently, the packing density of the solar battery elements 21 is reduced to such an extent that light is not fully effectively utilized for the signal transmission purpose. Further, nonuniformity of luminous intensity or irradiance distribution at the circular light receiving surface 23 results in mismatching of the electrical outputs of the individual elements 21, and this mismatching results, in turn, in a lowered total output of the photovoltaic part.